1. Field of the Invention
The present invention relates to closures for underground housings having surface access openings, and more particularly, to lids or caps for such openings.
2. Description of the Related Art
Utilities of various types are commonly buried underground. Such utilities include, for example, water, sewer, natural gas, telephone, cable television, irrigation, electric service, security and fire alarm service. Underground utilities commonly employ an access portal to allow service personnel to access the utilities for maintenance and meter reading. This access portal typically includes a pre-cast concrete box that is buried underground. Utility devices, such as valve mains, meters and wire connectors, are located within the concrete box. The box includes an opening through which the utility devices are accessed. When the box is not being accessed, the opening is covered by a lid. The lid and box are located such that the lid is flush, or nearly flush, with the level of the surrounding ground. The lid is typically made of pre-cast concrete or composite resin. The lid can include a lip that is shaped to engage the opening in the box. Alternatively, the opening of the box can be shaped to receive the lid, which does not have a lip.
A common configuration is a lid having tapered sidewalls, and a box having an opening with corresponding tapered sidewalls. In this configuration, the lid easily slides into the opening of the box and fixes itself firmly in place as the tapering sidewalls of the lid engage the tapering sidewalls of the opening. This design is relatively inexpensive to form and fairly robust, compared with more complicated closures.
While the concrete lids and boxes are quite strong, these lids tend to be heavy, and repeated opening of the box causes wear or damage. Operators, in opening and closing the box, tend to be careless in handling the lid. As the edges of the lid strike the edges of the box opening (or the ground), the concrete can chip or fracture on either one or both of the lid and the box. Over time, the lid may sustain too much damage to function properly, thereby requiring replacement of the lid. The box may also eventually reach a point where it must be replaced, as a result of damage to the opening therein. Replacement of the box can be costly and labor intensive, requiring the breaking of pavement in those cases where the box is under pavement. At the very least, the box must be excavated and replaced with a new box.
Additionally, in environments where freezing occurs, water may freeze between the lip of the sidewalls of the lid and the sidewalls of the box opening. In such an event, it is extremely difficult to remove the lid from the box. In extreme cases, the effort required to remove the lid from the box may be sufficient to destroy the lid.
Concrete lids are typically formed using a rubber mat and a sturdy aluminum dryer, which has a thickness on the order of 1 inch or more. FIG. 1 is a cross sectional view of an aluminum dryer 101, which is fitted into a corresponding rubber mat 102. Rubber mat 102 is placed flat on a platform 103. The upper surface of the rubber mat includes various raised sections 104, which create patterns and graphics on the upper surface of the lid. The outer edges of aluminum dryer 101 engage ridges on rubber mat 102, such that aluminum dryer 101 is held on rubber mat 102.
When creating lids, a reinforcing structure 105 can be set on rubber mat 102, within the perimeter of aluminum dryer 101. Reinforcing structure 105 includes a welded wire rack 106, which is supported by a set of four wheels 107. Wheels 107 are required to support wire rack 106 when wet concrete is poured into aluminum dryer 101. Reinforcing structure 105 is free-floating within aluminum dryer 101.
After aluminum dryer 101, rubber mat 102 and reinforcing structure 105 have been assembled, wet concrete 110 is poured into the upper opening of aluminum dryer 101 (and onto rubber mat 102). The concrete 110 is leveled off at the upper surface of aluminum dryer 101. The concrete 110 is then allowed to dry. When the concrete 110 has sufficiently set, rubber mat 102 is peeled off and the concrete 110, and embedded reinforcing structure 105, are removed from aluminum dryer 101 (typically by hammer). The removed concrete 110 and reinforcing structure 105 form a concrete lid. Aluminum dryer 101 is then cleaned, typically by scraping off any excess dried concrete. The process is then repeated, reusing aluminum dryer 101 and rubber mat 102.
This process has several disadvantages. First, as described above, the process is labor intensive. In addition, the number of lids that can be produced at a time is limited by the number of aluminum dryers. The aluminum dryers are expensive and take up significant storage space, thus providing a practical limitation on the number of aluminum dryers that can be used. Moreover, the rubber mats shrink over time, thereby resulting in irregular edges around the upper surface of the resulting lids. The rubber mats primarily shrink at the edges where the rubber mat contacts the aluminum dryer. The different coefficients of expansion/contraction between rubber mat 102 and aluminum dryer 101 contribute to this shrinkage. The rubber mat shrinkage can also cause the patterns/printing formed on the upper surface of the lid to be raised or recessed with respect to the upper surface of the lid, thereby creating a tripping hazard. Eventually, the rubber mats degrade to a point where they must be replaced. In addition, reinforcing structure 105 is relatively expensive, as this is a separate multi-piece element that must be manually inserted into aluminum dryer 101. Finally, the edges of the resulting lid are concrete. As a result, these edges are susceptible to chipping and cracking when the lid is inserted and removed from the concrete box. Moreover, these edges can chip or crack at the time of manufacture, thereby causing these lids to be thrown away and raising the cost of production.
Some concrete lids have been created using a sheet metal form. FIG. 2 is a view of a conventional sheet metal form 201, which is fitted into a corresponding rubber mat 202. Rubber mat 202 is placed flat on a platform 203. Again, the upper surface of rubber mat 202 includes various raised sections 204, which create patterns and graphics on the upper surface of the lid. The outer edges of metal form 201 engage ridges on rubber mat 202, such that metal form 201 is held on rubber mat 202.
Metal form 201 is significantly thinner than aluminum dryer 101. For example, metal form 201 may be formed from a steel galvanized sheet metal having a thickness of about 1/16 inch. Metal form 201 includes tapered sidewalls 201A and a lattice structure 201B continuous with the sidewalls 201A.
After metal form 201 and rubber mat 202 have been assembled, wet concrete 210 is poured through the lattice structure 201B into metal form 201 (and onto rubber mat 202). The concrete 210 is leveled off at the upper surface of metal form 201. The concrete 210 is then allowed to dry. When the concrete 210 has sufficiently set, rubber mat 202 is peeled off, thereby completing fabrication of the lid. Metal form 201 remains intact on the completed lid.
This process also has several disadvantages. First, metal form 201 is created using a five-step process, with one of these steps requiring the use of a 30-ton press. As a result, metal form 201 is relatively difficult and expensive to fabricate (on the order of $3.25 per form). Moreover, because metal form 201 is not as heavy as aluminum dryer 101, the wet concrete tends to displace metal form 201 on rubber mat 202, such that some concrete seeps under the metal form, as illustrated at locations 211 and 212. This concrete readily chips, thereby contributing to an irregular edge at the upper surface of the lid. This problem worsens as rubber mat 202 shrinks over time. In addition, lattice structure 201B, which functions to maintain the shape of metal form 201 during the concrete pour (and drying), does not provide any significant reinforcement to the resulting concrete lid (largely because this lattice structure 201B is located at the bottom of the lid). Moreover, the portions of concrete 210 immediately adjacent to lattice structure 201B are susceptible to chipping.
Lids have also been made from composite resin. Composite resin lids are lighter and less susceptible to chipping and cracking than concrete lids. However, composite resin lids are significantly more expensive than concrete lids. More specifically, a composite resin lids will typically be two to three times more expensive than a concrete lid of similar size. Moreover, composite resin lids are a petroleum-based product. Thus, the cost of composite resin lids is ultimately based on the price of petroleum. In addition, composite resin lids have a tendency to discolor in response to extended exposure to the sun.
It would therefore be desirable to have a low-cost, durable lid for utility closures that overcomes the above-described deficiencies of the prior art.